I have no interest in Green Tree Data Message Service, nor do I work for them or anything else. Your report just happened to grab my attention. I was able to find the following information by searching the business name, using any of the search engines out there, the one I used begins with "G". It took me less than 20 seconds to find their contact info, so your statement of "I can't reach them by phone, and there is no website at the address given." is a bunch of BS. Here is the info I found for you - now you can contact them directly and handle your problem directly with them.
GREEN TREE DATA - ABOUT US
With Green Tree Data Message Service, you can check your messages from anywhere in the United States. Your friends and family will be able to leave you messages using your own toll-free number.
Green Tree Data Message Services can also send reminder calls and wake-up calls from anywhere in the continental USA. No credit check or long-term contract is required and you can cancel at any time by calling toll-free 1-800-215-1961.
Green Tree Data Long Distance Services allows you to make Unlimited Long Distance calls from any phone, anywhere at any time for ONE Low Price!
You will simply be billed a low monthly service fee of $8.23 that will be included on your phone bill. In order to program and activate your service, there is also a one-time set-up fee of only $8.43. All charges will appear on your local telephone on the Transaction Clearing bill page as being billed on behalf of Green Tree Data. The fee is 100% refundable if you are not completely satisfied with our service!
For Questions or Cancellation? Call customer service toll-free at 1-800-215-1961 or write to Green Tree Data at PO Box 50480, Minneapolis, MN 55405.
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Good luck to you, hope you are able to use this information to get your problem with them resolved.
Have a great day!